W. Ebel et al., A conserved domain in Escherichia coli Lon protease is involved in substrate discriminator activity, J BACT, 181(7), 1999, pp. 2236-2243
Lon protease of Escherichia coli regulates a diverse set of physiological r
esponses including cell division, capsule production, plasmid stability, an
d phage replication. Little is known about the mechanism of substrate recog
nition by Lon. To examine the interaction of Lon with two of its substrates
, RcsA and SulA,,ie generated point mutations in lon which affected its sub
strate specificity. The most informative ion mutant overproduced capsular p
olysaccharide (RcsA stabilized) yet was resistant to DNA-damaging agents (S
ulA degraded). Immunoblots revealed that RcsA protein persisted in this mut
ant whereas SuLA protein was rapidly degraded. The mutant contains a single
-base change within ion leading to a single amino acid change of glutamate
240 to lysine, E240 is conserved among all Lon isolates and resides in a ch
arged domain that has a high probability of adopting a coiled-coil conforma
tion, This conformation, implicated in mediating protein-protein interactio
ns, appears to confer substrate discriminator activity on Lon, We propose a
model suggesting that this coiled-coil domain represents the discriminator
site of Lon.